In the production of pulp according to the sulphate pulp method wood, in the form of chips, is delignified in an alkaline solution, which mainly consists of NaOH and NaHS, in a pressurized cooking process, which in the final stage normally has a temperature in the range of 150.degree.-175.degree. C. The ratio of hydroxide ions [OH.sup.- ] to [HS.sup.- ] is normally within the range of 25-40% sulphide [2HS.sup.- ], calculated on the sum of the contents of sulphide ions and hydroxide ions.
An increased content of sulphide ions in relation to hydroxide ions in the cooking liquor increases the yield of pulp and, normally, improves the important properties of the final product. In the beginning of the cooking process, the so called impregnation stage, an increased proportion of sulphide ions forms the bases of a more efficient release of lignin during the actual cooking process. A simultaneous reduction of the contents of hydroxide ions decreases the degradation of cellulose, which results in an increased yield and higher quality of the final product.
The present invention provides a white liquor having enhanced sulphidity, which can be utilized in the above mentioned cooking process.
Further, the invention provides white liquor having reduced sulphidity. White liquor having reduced sulphidity may e.g. be used as a chemical in the production of bleached wood pulp.